Large flat panel displays and other electronic devices generally are manufactured by a series of process steps in which successive layers of material are deposited on a workpiece, such as a glass substrate, and then patterned. Some of the deposition steps typically are performed by sputter deposition, which is deposition by sputtering material from a target.
In sputter deposition, the sputtering target and the workpiece are positioned within a vacuum chamber in which a gas having relatively heavy atoms, such as argon, is excited to a plasma state. A negative DC or alternating voltage on the target accelerates the argon ions from the plasma to bombard the target. Some of the bombardment energy is transferred to material on the surface of the target, so that molecules of target material are ejected or "sputtered" from the target. The workpiece is positioned so that a large portion of the sputtered target material deposits on the workpiece.
Some types of commonly used targets tend to produce particles of contaminants that can ruin the electronic device being manufactured if the particles are allowed to fall on the workpiece. For example, indium tin oxide (ITO) targets typically contain at least one percent impurities. As the target is sputtered, the impurities can agglomerate into particles as large as 1 mm before they fall off the target. Another type of target that tends to produce particles of contaminants is a target constructed as a matrix of tiles instead of as a single, monolithic target. Arcing in the gaps between tiles can dislodge particles of the material used to bond the tiles to a backing plate.
The problem of contaminant particles falling on the workpiece is most severe when the target and workpiece are both oriented horizontally, with the target directly above the workpiece. In that case, almost all particles that fall off the target will lodge on the workpiece.
To overcome this problem, some conventional sputter deposition chambers orient the target and the workpiece vertically, with the workpiece alongside rather than below the target. In such designs, most particles that fall off the target will harmlessly fall below the target rather than onto the workpiece. However, it is difficult to mechanically support a large glass substrate in a vertical orientation without excessively stressing and even cracking the substrate.
Therefore, a need exists for an apparatus and method for sputter depositing material on a workpiece that minimizes the deposition of contaminant particles on the substrate and that can be performed with a horizontally oriented substrate.